Analysis of polycyclic aromatic hydrocarbons in heterogeneous samples

Chanan Sluszny, Vladimir V. Gridin, Valery Bulatov, Israel Schechter*

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

10 Scopus citations

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) have long been recognized as toxic, ubiquitous materials, classified by environmental agencies as priority pollutants. These toxic materials are found in soil and waters at high concentrations that are usually attributed to anthropogenic sources. Based on these known facts, the rapid analysis of PAHs is of current interest. Current methods, which are based on the collection of samples and their analysis by conventional laboratory procedures, are time consuming and may cause sample contamination prior to analysis. Direct measurement of soil and water on-site addresses these problems directly. The resulting feedback can immediately be used to direct further sampling and analysis, leading to time saving, accurate and even less expensive site characterization. Unfortunately, natural materials, found in water and soil, greatly reduce sensitivities of on-site techniques. Thus, at present, these methods are only capable of a semi-quantitative analysis when applied to "real world" samples. Prime goals of this research were, therefore, to develop new methods, which bring about the possibilities of direct and on-site analysis of PAHs within such heterogeneous environments as soil and water resources. In this study the analysis of particulate PAHs (i.e., soil pollution) was based on the newly developed Fourier Transform Spectral Imaging Microscopy (FT-SIM) set-up. This method enables direct detection and characterization of PAHs micro-particles. The method is fast (1-5 minutes depending on the amount of contaminant) and requires no laborious sample preparation. Linear regression plots were obtained for PAHs embedded onto sand particles. Limits of detection (LOD) of approximately 2 pico-gram (pg) were obtained for mono-components and for simple PAH mixtures. This corresponds to bulk concentrations in the ppm range, thus indicating the capabilities of the method to handle concentrations of PAHs in environmental relevant samples. The absolute detection limits of FT-SIM are even lower. Taking into account the instrumental/optical resolution of this technique, the analysis of 1 micron particles, which corresponds to a mass of approximately 0.5 pg, is feasible. However, it has been concluded that reliable monitoring of PAH contamination requires further investigation of several features inherent to the microscopic imaging analysis itself. For such purpose, single crystals of several PAHs were grown and their fluorescence characteristics were analyzed. Various morphology-related features were found to affect analysis. These include effects associated with either the crystal edge or the crystal surface originated spectra, and physical processes related to inter-crystal self-absorption of emitted fluorescence. In addition, the crystal-alignment towards the microscope objective was shown to affect the read-outs of the spectral imaging utility. Since quantification by FT-SIM is based on measurements of the emitted fluorescence, such effects could influence analysis. Still, it was demonstrated that proper statistical sampling, which includes analysis of large batches, results in good correspondence between fluorescence intensity and the actual particulate mass. Furthermore, it was shown that FT-SIM can handle the monitoring of inhomogeneous PAH-particulate materials. Such capabilities are of great importance for PAH contamination originated from various industrial activities. Moreover, it was shown that FT-SIM is suitable for direct analysis of photochemical effects associated with PAH crystallites. However, FT-SIM cannot handle analysis of PAH solutions, i.e., water pollution. For such cases, we applied a polymer-mediated technique. The method is based on selective entrapment of PAHs into polymer films. The capability of this method for direct analysis of polluted water was demonstrated by using humic substances and clay suspensions as interfering compounds. These were shown to have an insignificant effect on PAH analysis. Moreover, the attachment of such polymer films to a remote laser induced fluorescence probe, resulted in LOD in the range of parts per-trillion (ppt), for PAHs solutions containing either humic substances or clay suspensions. These LOD are approximately 2-3 orders of magnitude better than those of the conventional fluorescence probe, i.e., the probe without the polymer films.

Original languageEnglish
Pages (from-to)77-165
Number of pages89
JournalReviews in Analytical Chemistry
Volume21
Issue number2
DOIs
StatePublished - 2002
Externally publishedYes

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